Month: September 2018

Yesterday was nice. It wasn’t perfect, no, but it’s a start on our road to autumn. Unfortunately, like many Houston freeways, the road there is still under construction. More on that in a second. First, some news.

NOAA has completed their analysis of rainfall return period in Texas. Those maps we’ve utilized for 100 and 500 year floods are now officially obsolete. In the Houston area, a 24 hour rainfall of around 13″ used to be required to classify a rainfall event as a “100-year flood.” Remember a “100-year flood” is a flood that has a one-percent chance of occurring in any given year. That 13″ rainfall has been revised up to 18″ of rain in 24 hours to qualify as a 100-year flood. Basically, what we used to define as a 100-year flood is now a 25-year flood. I think most of us knew this already; it had been telegraphed last year, but we can now make it official.

Why is this changing? The previous maps are decades old. The primary reason is that we have more data and better data to work off of. We also know, based on plenty of data, that rain events are getting bigger in Texas, and this is especially disproportionately true in the Houston-area. Ultimately, there will be ramifications because of these map changes. Infrastructure is built to these map standards. Floodplain regulations are based on these map standards. These changes have been well-telegraphed since Harvey, so some of this process is already underway. But it’s a slow process, so don’t expect changes next month. It’s a start, however.

On to the weather…

Today

Radar is mostly quiet this morning, though we are beginning to see a few showers near the coast as of 5:30 AM. More noticeably, we still see a good deal of cloud cover in the area.

A satellite loop shows low clouds (white), mid-level clouds (yellow), and high clouds (dark colors) moving through the area this morning. Sunshine will be at a premium, especially southeast of Houston today. (College of DuPage)

On the loop above, the bright white indicates lower stratus clouds and the darker colors indicate higher cirrus clouds. The yellow offshore indicates showers and mid-level clouds. Bottom line: We have a lot of clouds around, so sunshine will be limited today, especially south and east of Houston.

As the day goes on, we expect to see scattered showers and storms develop, initially near the coast and spreading a bit further inland as yesterday’s cold front begins to return as a warm front. Look for high temperatures today to hit the low-to mid-80s.

Well, the front made it through. It’s not a strong front, and it won’t last too long, but at least it should clear out our weather for a day or a bit longer. I guess we’ll have to take what we can get after such a soggy September.

Thursday

This should be a pretty nice day, with highs only in the low- to mid-80s, albeit with partly to mostly cloudy skies. Light northerly winds will bring some drier air into the region as well, and this should keep rain showers mostly at bay—although we can’t rule out some lingering activity along the coast. Low temperatures tonight will probably be the coldest they’ve been this fall, with the northern half of Houston likely falling just below 70 degrees. Again, this isn’t a particularly strong front for late September, but this evening will probably feel pretty nice outside.

Friday

After the cooler start, the region will see the return of moisture from the Gulf of Mexico on Friday, and this should allow some showers and thunderstorms to start spreading into coastal areas, and possibly inland later in the day. With partly sunny skies and highs in the mid-80s, we don’t expect anything too widespread or too heavy in terms of rainfall.

Thunderstorms popped up along the coast early this morning, and now some of the heavier rains have migrated inland. These pre-sunrise storms reflect what is likely to be a messy forecast for the next several days as a weak cold front pushes into the area, just beyond Houston offshore, and then likely moves backward through Houston. Add it all up, and there will be a healthy chance of storms over the next several days—along with a brief interregnum of drier and cooler air. Hopefully.

Wednesday

This morning’s storms are likely a precursor for showers and thunderstorms moving along a front that, near sunrise, is approaching the Interstate 35 corridor in central Texas. This should lead to elevated rain chances this afternoon and evening across most of the metro area, with storms moving from northwest to southeast. In terms of accumulation, most areas will probably see 0.5 to 1.5 inches of rainfall between Wednesday and Thursday morning, which could cause some brief problems on roadways but should for the most part be manageable.

Thursday

Some drier air should work its way into Houston behind the front, especially for areas well to the west and north of downtown Houston. Lows in the 60s are possible for these areas, but unlikely within Harris County or the city of Houston itself.

Any reprieve won’t last long, however, as the front should lift back onshore Thursday, likely leading to elevated rain chances during the afternoon or evening hours. (We do not expect these storms to be as heavy as those on Wednesday). Daytime highs on Thursday should be in the low- to mid-80s, and we sincerely hope everyone enjoys their 12 hours of almost fall-like weather. Not that we’re bitter about the lack of a strong fall cold front, or anything.

All things considered, after a long, hot, and wet summer, Monday was pretty nice. We had ample sunshine, highs in the upper 80s, and some drier weather. It offered an all-too-brief taste of what is eventually coming—fall, which may arrive toward the end of the first week of October. But now it’s over and we’re headed back into a wet and humid period for awhile. We’re not too concerned about the potential for flooding this week, but the dreary quotient for the next several days will be pretty high.

Tuesday

As Gulf moisture resumes flowing into the region today, rain showers will also spread over the area. I’d peg rain chances at about 50 percent today, with mostly cloudy skies and highs in the upper 80s. Fairly quick movements of storms should limit any concerns about heavy rainfall lasting too long.

Wednesday and Thursday

The midweek is … interesting. As a cold front approaches the area from the northwest, rain will probably spread throughout much of the region on Wednesday. It’s not clear whether the front itself will reach into Houston, or stall just before or after pushing into the region. If you’re lucky (and if you’re on the west side of the city), you may see a day or so of drier weather on Thursday. But it’s not something I’d count on.

Cold front position at 10pm Wednesday, per the NAM model. Will it push any further to the east? (Weather Bell)

Basically, we can expect rainfall ahead of and along the front, and some brief drying after the front if it pushes through where you live. However, even if it does, the front will probably pull back (westward) across the region on Friday. Highs in the mid- to upper-80s.